From 4 letters ab18 one can make all 18 numbers with 4 digits. (In a number, each digit is written only once.) The sum of all 18 possible numbers is 90216. Find a and b.
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12 tháng 10 2016
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4) The fourth power of 3 is \(64\)
5) Twice the square of 3 \(18\)
6) The number of ethnic group in Vietnam? \(54\)
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LD
22 tháng 1 2018
Tell the numbers to find are \(\overline{ab}\)
\(\Rightarrow\left\{{}\begin{matrix}2b-a=1\\\overline{ab}-\overline{ba}=27\end{matrix}\right.\)
=> 10a + b - 10b - a = 27
=> 9a - 9b = 27
=> a-b = 3
=> a = b + 3
=> 2b - 1 = b+3
=> 2b - b = 3 + 1
=> b = 4
=> a = \(2\cdot4-1=7\)
So he number to find is 74